My husband did, and then said that if I ever bought chicken liver for DD's food again, he was going to throw it away! He didn't just add it in, though, it was a full meal of some sort we made and then pureed.
If you're looking for added iron, egg yolk (cooked!), brewer's yeast, and blackstrap molasses are all good additives. But yes, I would certainly cook chicken livers before giving them to anyone.